This disclosure relates generally to the usage of radiation detectors and gamma-ray detectors in a downhole tool and, more particularly, to pulse counting for a formation density tool.
This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present techniques, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light and not as admissions of any kind.
To locate and extract oil, water, natural gas, or other liquids, a hole, referred to as a borehole, may be drilled into a surface of a geological formation. To form the borehole, a drill bit may excavate a portion of the geological formation. A drilling fluid, commonly referred to as “mud” or “drilling mud,” may be pumped into the borehole, for example, to cool and/or lubricate the drill bit. Generally, the drilling mud may include solid particles, such as dirt, suspended in liquid, such as water. When the geological formation is porous, the liquid component of the drilling mud may be pushed into the geological formation, leaving the solid particles on the borehole wall. Over time, a layer of the solid particles, commonly referred to as “mud cake,” may form along the wall of the borehole.
A formation density tool may be deployed sub-surface to measure physical properties of a surrounding geological formation. The formation density tool may be moved within a borehole drilled in the geological formation. For example, the formation density tool may be pushed to move the formation density tool farther into the borehole and/or pulled to remove the formation density tool from the borehole. The formation density tool may include a source to emit high-energy photons into the geological formation. Some of the high-energy photons may interact with the geological formation and may then be detected by one or more detectors in the formation density tool. The physical properties of the geological formation may be determined from the characteristics of the detected high-energy photons.
As the formation density tool is used to measure physical properties of the geological formation, an energy spectrum of the signal of the high-energy photons detected by a detector may be distorted for a variety of reasons, such as a change in temperature at the detector, a change in voltage on the detector, or the like. Radioactive stabilization sources may be used to determine such changes in the spectral response of the formation density tool. A process referred to as gain regulation may be used to account for such changes (e.g., to account for the changes in temperature, changes in voltages, etc.). In some cases, such determination may be used to adjust energy scale and spectral binning without attempting to adjust system gain. Radioactive stabilization sources may emit photons of specific energy that do not interfere unduly with the measured energy spectrum from the high-energy photons. However, the use of radioactive materials may be heavily regulated, thereby causing a burden to deploy such sources in a formation density tool.